In many applications it is desirable to limit physical access to electrical circuits and additionally to minimize the risk that the circuit is accidentally energized while it is being accessed. Accidental activation of an electrical circuit during servicing, for example, can result in death or physical injury to personnel as well as damage to expensive equipment.
Physical access to an electrical circuit, such as a power transformer, is typically controlled by enclosing the circuit in a cabinet or housing. Such cabinets often have access doors which can be locked with an integral lock or a padlock. In order to prevent continued activation of the circuit when the cabinet doors are opened, it is known to provide proximity switches for deactivating the circuit in response to the cabinet doors being opened. However, such safety systems can easily be circumvented by short circuiting the switch or biasing the switch to its closed position.
Additionally, it is known to provide devices for physically maintaining a main power switch or circuit breaker in its off position. Two such systems are disclosed in Nat U.S. Pat. No. 4,440,994, issued Apr. 3, 1984, and Sahrbacker U.S. Pat. No. 4,705,920, issued Nov. 10, 1987. The Nat patent describes a pivoted actuator switch having a lock to prevent the switch from being turned to the "on" position without insertion of a removable key member. The Sahrbacker patent describes a slidable electrical contact carrier actuated by a rocker type actuator which includes a removable locking key as a part of the actuator assembly. Removal of the key in the Sahrbacker device prevents movement of the carrier and thus prevents actuation of the switch. These devices suffer from at least two drawbacks. First, manufacture of these devices is complicated and costly because both patents incorporate specially manufactured locks and/or components. Second, neither system can readily be adapted to limit physical access to the electrical circuit.
It is an object of the present invention to provide a safety apparatus which controllably maintains an electrical power switch in its off position.
Another object of the present invention is to provide a safety apparatus which inhibits access to an electrical circuit when the circuit is deactivated.
A further object of the invention is to provide a safety lockout which is both simple and economical to manufacture.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.